The present invention relates to a method for operating a fuel supply system for an internal combustion engine in a motor vehicle in particular, with a quantity of fuel to be supplied to a cylinder being determined, and with the quantity of fuel to be supplied being injected by an injection valve. In addition, the present invention relates to a fuel supply system for an internal combustion engine in a motor vehicle in particular, having a control unit for determining a quantity of fuel to be supplied to a cylinder and having an injection valve for injecting the quantity of fuel to be supplied.
Increasing demands are being made of internal combustion engines in motor vehicles, for example, with regard to reducing the fuel consumption and the exhaust gases produced while achieving the desired high performance at the same time. To this end, modern internal combustion engines are equipped with a fuel supply system with which the supply of fuel to the combustion chamber of the internal combustion engine is controlled and/or regulated electronically, in particular with a computer-assisted control unit. It is possible to inject the fuel into an air intake manifold of the internal combustion engine or directly into the combustion chamber of the internal combustion engine.
With the type of fuel injection mentioned last, also known as direct fuel injection, the fuel must be injected into the combustion chamber under pressure. To this end, a pressurized storage is provided, where the fuel is pumped by a pump and put under a high pressure. From there, the fuel is injected directly through injection valves into the combustion chambers of the internal combustion engine. In homogeneous operation, the start of injection is during the intake phase of the respective cylinder, while in fuel saving stratified operation, injection takes place during the compression phase.
The quantity of fuel to be injected through the injection valves directly into the combustion chambers of the internal combustion engine, plus optionally also the start and/or the end of injection, are determined by the control unit first in both modes of operation mentioned as a function of a plurality of performance quantities of the internal combustion engine. Then the injection valves are controlled by the control unit in accordance with the values thus determined.
Special starting procedures are provided for starting an internal combustion engine. At low outside temperatures in particular, the quantity of fuel to be injected must be increased in the initial injection in comparison with an internal combustion engine at operating temperature. This is necessary so that a sufficient quantity of low-boiling fuel components will be available in startup for an ignitable fuel-air mixture. Likewise, an increased quantity of fuel is necessary in startup to build up a fuel film on the inside walls of the cylinders. In the subsequent injections, this increased quantity of fuel to be injected is reduced back to the standard quantity of fuel to be injected for the internal combustion engine at operating temperature.
With the other type of fuel injection mentioned above, known as intake manifold injection, fuel is injected by an injection valve into the intake manifold of the internal combustion engine. Increased quantities of fuel are again necessary in startup to build up a fuel film, inter alia, on the inside walls of the intake tube.
It is possible that the quantity of fuel supplied to a cylinder in starting the internal combustion engine might not actually be burned. In this case, the unburned fuel goes into the exhaust pipe, inter alia. This can lead to increased emissions of pollutants, and to increased levels of unburned hydrocarbons in particular.
An object of the present invention is to provide a method of operating a fuel supply system and a fuel supply system for an internal combustion engine to permit detection of increased pollution emissions.
The object is achieved with a method and a fuel supply system of the type defined in the preamble according to the present invention in that a test is performed to determine whether combustion has taken place in the cylinder and the quantity of fuel supplied to the cylinder where no combustion has taken place is determined.
The quantity of fuel thus determined is the quantity of unburned fuel. It can enter the exhaust pipe, where it leads to increased emission of pollutants. The quantity of fuel thus determined is a value representing the possible pollution emissions. Thus increased pollution emissions can be detected on the basis of the quantity of fuel determined. For example, this information can be used by the control unit as part of error diagnosis or the like.
In an advantageous refinement of the present invention, the quantity of fuel determined is added up. In this way, additional injections into other cylinders of the internal combustion engine which do not lead to combustion in these cylinders are also taken into account by the present invention. It is thus possible to detect possible pollution emissions even more accurately on the basis of the quantity of fuel added up.
In another advantageous refinement of the present invention, the quantity of fuel added up is weighted. Through the present invention, this takes into account the fact that only a portion of the total unburned fuel, not the entire amount, leads to increased pollution emissions. It is thus possible to determine the possible pollution emissions of an internal combustion engine even more accurately on the basis of the weighted quantity of fuel.
In an advantageous embodiment of the present invention, the weighted quantity of fuel is compared with a limit value, and if the limit value is exceeded a faulty starting procedure is deduced. The maximum allowed quantity of unburned fuel is determined on the basis of the limit value. Through the present invention, the quantity of unburned fuel entering the exhaust pipe, optionally the quantity of unburned fuel added up and optionally the weighted quantity of unburned fuel is compared with this limit value. Thus, it is possible with this control unit to reliably detect increased pollution emissions.
In an advantageous refinement of the present invention, the test of whether combustion has taken place is conducted as a function of one or more of the following performance quantities of the internal combustion engine:
an increase in temperature of the respective cylinder or all cylinders,
an increase in pressure in the respective cylinder,
an increase in rpm of the internal combustion engine,
the lambda value of the exhaust gas of the respective cylinder or all cylinders, obtained by a probe evaluating the oxygen partial pressure,
the quantity of unburned fuel in the exhaust gas of the respective cylinder or all cylinders,
changes in ignition voltage.
With these performance quantities of the internal combustion engine, it is possible to determine by a simple method whether or not combustion has taken place in one of the cylinders. For example, if the temperature of a certain cylinder increases after firing of that cylinder""s sparkplug, it can be concluded that this firing of the sparkplug has led to ignition of the air-fuel mixture in this cylinder and thus to actual combustion.
It is especially advantageous if a test is performed to determine whether the starting procedure was successful, and if the starting procedure has been successful, the quantity of fuel is compared with the limit value. For example, if a certain rpm threshold is reached or exceeded, this means that the starting procedure has been concluded successfully. In this case, the question of whether or not the starting procedure was faulty with regard to the quantity of unburned fuel entering the exhaust pipe can then be reviewed.
Likewise, it is especially advantageous if a test is performed to determine whether the starting procedure has been terminated, and if the starting procedure has been terminated, the quantity of fuel is compared with the limit value. In this case where the starting procedure has not been concluded successfully, the question of whether or not the terminated starting procedure was faulty with regard to the quantity of unburned fuel entering the exhaust pipe can also be reviewed.
The implementation of the method according to the present invention in the form of a control element provided for a control unit of an internal combustion engine in a motor vehicle in particular is especially important. A program that is capable of being run on a computing device, in particular a microprocessor, and is suitable for executing the method according to the present invention, is stored on the control element. Thus in this case, the present invention is implemented by a program stored on the control element, so that this control element provided with the program represents the present invention in the same manner as the method carried out with the program. The control element may be in particular an electric storage medium, e.g., a read-only memory.